Residents and businesses in the Lehigh Valley and Poconos are being asked to reduce their water usage by 10 to 15 percent to combat a drought warning issued Thursday by the state Department of Environmental Protection.

A lack of rain in the eastern United States has led to "extremely low stream flow and groundwater levels" in portions of the Delaware River Basin that include Lehigh, Northampton, Carbon and Monroe counties, the agency chief said in a statement.

"We're asking residents and businesses, particularly in central and eastern counties to use water wisely and follow simple water conservation tips to ease the demand for water," DEP Acting Secretary Patrick McDonnell said in a statement. "We suggest that public water systems that implemented water restrictions this summer continue them to preserve their drinking water supplies."

More counties in central Pennsylvania also were added to the state's drought watch list due to persistent dry conditions and are asked to conserve water by 5 percent, DEP said.

A drought warning is the final designation governments give communities before they issue mandatory conservation programs to conserve water supplies. A watch is a notch above a warning level.

The Lehigh Valley and Poconos are the only four counties in the state to get the higher warning. The lower watch list includes Bucks, Montgomery and Philadelphia counties and stretches west to cover all counties in the Susquehanna River Basin.

Other sections of Pennsylvania are wetter. Counties west of the Appalachian Mountains and along the northern tier have above-average precipitation levels that have improved surface and ground water levels, DEP said.

Drought conditions are monitored by the federal and state governments and private water supplies that track soil moisture, rain, groundwater, stream flow and reservoir levels, said Dennis Risser, a hydrologist at the U.S. Geological Survey Water Science Center in New Cumberland, Cumberland County.

"This dryness is all through out the northeast right now," Risser said. "If you look at our maps it goes well up into the New England states."

With 0.22 inches of rain, May has become the second driest month on record.

With 0.22 inches of rain, May has become the second driest month on record.

Summertime rain does little to recharge groundwater, he said, because vegetation and root systems take most of the precipitation. The best time to replenish the groundwater through soaking rains and heavy snow is from November to April, he said.

As of Friday, USGS's 43-year-old groundwater gauge in Lehigh County recorded some of its lowest levels in its history. It's only been this low between 5 and 10 percent of the time, Risser said.

Since Jan. 1, precipitation was 7.4 inches below normal at the National Weather Service's official rain and snow gauge at Lehigh Valley International Airport. Total normal precipitation for this time of year is 38.6 inches.

Thursday's rain showers in the Valley briefly raised levels along the Little Lehigh Creek and Monocacy Creek in Bethlehem, according to online USGS records. But those streams remain far from normal on Friday, records show.

Looking at small streams is good way to visually see proof of low water levels, said James Campbell, director of the USGS Pennsylvania Water Science Center. But, larger rivers, like the Delaware, should not be used to gauge drought effects, he said.

"It's very misleading to look at the Delaware," Campbell said, because its height and flow are augmented by reservoir releases up stream in New York.